1. Field of the Invention
The present invention relates to a method of printing with an ink jet printer, and, more particularly, to a method of printing near an end of printable area on a print medium.
2. Description of the Related Art
Ink jet printers typically include a paper feed mechanism that moves a print medium through a print zone. The print zone corresponds to the height of the printhead(s). As the print medium is advanced into the print zone, the printhead prints a section of the page by firing nozzles as the printhead moves across the width of the page. The print medium is advanced a predetermined amount, and then the printhead prints again while moving horizontally across the page. This process of advancing and printing while scanning continues down the entire printable area of the print medium.
Movement of the print medium into the print zone is typically controlled by feed rollers which are positioned prior to the print head. While the print medium is under these feed rollers, the print medium advance is accurately controlled. However, near the end of the printable area (also called an image area) at the bottom of the print medium, the print medium exits these feed rollers and movement through the print zone may not happen at all; or in the case of secondary exit rollers, the advance movement becomes much less accurate. Either of these situations may cause noticeable and objectionable print quality defects if printing continues after the paper has left the control of the feed rollers. While mechanical design improvements can limit the bottom portion of the page which suffers from this advance movement and inaccuracy, it is usually cost prohibitive to completely eliminate via mechanical solutions.
One technique which may be used to improve advance movement and accuracy is a software solution which controls and limits which portion of the printhead is used at the bottom of the page. For example, the printhead may be advanced using the predetermined advance amount until the bottom of the printhead is adjacent the end of the printable area. The printhead is then scanned one or more times adjacent the end of the printable area without advancing the print medium so that the print medium does not leave the control of the feed rollers.
The software solution described above to reduce print defects near the end of printable area may also be utilized during multiple pass printing, such as with known dithering or shingling techniques. Multiple pass printing typically uses different nozzles of a printhead to place ink dots at selected ink dot locations on a raster line over multiple passes or scans of the print head across the print medium. A multiple pass printing technique reduces print defects, such as may be associated with a clogged nozzle or the like, by using different nozzles in different passes of the printhead.
When the software technique described above for stopping advance of the print medium near the end of printable area is used in conjunction with a multiple pass printing technique as also described above, the same nozzles of the printhead are used during the multiple passes of the printhead across the print medium. Thus, the multiple pass printing no longer has the advantage of avoiding print defects associated with a clogged nozzle or the like, and print degradation may occur near the end of the printable area in the region where the print medium is no longer advanced relative to the printhead.
What is needed in the art is a method of printing with an ink jet printer near and end of printable area which minimizes possible print degradation near the end of the printable area.